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The Electron launch vehicle first stage has nine Rutherford engines In addition to adapting the single-engine-out-friendly nine engine configuration from the Falcon-9, the rocket carries a significant mass of batteries in order to power two electric motor-driven propellant pumps for fuel and oxidizer.

For a given amount of work (Joules) the lower energy density (Joules per kilogram) of electrical batteries means they are something like 50 times heavier than the LOX/RP-1 needed to do the same work.

The tradeoff is simplicity versus newness of technology and battery mass. Newness did not seem to be a problem (highly reliable electric motor driven pumps in hostile environments are a mature technology on Earth) and the battery mass can be at least party offset by dropping spent batteries ("battery staging").

Question: Does electric fuel pumping scale well for rockets? Is the Electron at a "sweet spot" in terms of size, or would smaller and (much) larger rockets see similar tradeoffs (qualitatively and quantitatively) if going the electric fuel pump route?


Related background:

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    $\begingroup$ Just a guess: the power requirements to pump the fuel needed for something like an F1 or even just a Raptor likely make it infeasible. Neutron is going to have turbopump-fed engines, so at least Rocket Lab itself seems to have doubts. The allure of electric pumps is the simple startup (no "chicken and egg" problem), throttle ability down to 0 (for the pump side at least, obviously combustion must still be sustained), and the ability to completely drain the tanks. $\endgroup$ Sep 6 at 11:05
  • $\begingroup$ @JörgWMittag naively I would think that it would scale up at least quite nicely, i.e. linearly; 10x more massive rocket with 10x the fuel needs 10x bigger pumps and 10x bigger batteries. I can't think of any reason why it wouldn't. What makes you think "the power requirements to pump the fuel needed for something like an F1 or even just a Raptor likely make it infeasible"? What am I missing? $\endgroup$
    – uhoh
    Sep 6 at 22:40
  • $\begingroup$ I just played around with some numbers. You would need 2.85 Tesla Megapacks to store the energy required to power the turbopumps for the 5 F1 engines of the Saturn V first stage. That's 2.85 shipping containers weighing 65 tons. However, they are not designed to dump all of that energy within 2.5 minutes! Based on the maximum power output of a Megapack, you would need 133 Tesla Megapacks in parallel to provide the necessary power. Now, we can probably improve on that by making the batteries non-rechargeable, and by optimizing them for peak power draw, but still, that's a lot of mass. $\endgroup$ Sep 7 at 7:59
  • $\begingroup$ And that's just for the batteries. Electrical motors of the required power are used to power the largest wind tunnels, compressors on offshore gas platforms, submarines, or frigates. I randomly found this company: jeumontelectric.com/en/products/synchronous-machines/motors Assuming that's their biggest model (40MW) in the photo, that would be just enough to power one of the 5 turbopumps of our hypothetical Saturn V E. $\endgroup$ Sep 7 at 8:37
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    $\begingroup$ I can image a two-stage design: battery powers a electric pump that feeds the turbine, and the turbine pumps the main engine. This way you more or less get the performance of a closed-cycle with the complexity of an open-cycle. $\endgroup$ Sep 8 at 3:48

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